Murphy led businessman Rod Blum 51 percent to 40 percent according to the poll conducted by Myers Research and Strategic Services for Murphy's campaign. The lead was outside the 4.9 percent margin of error.

Murphy also led Blum among self-identified independents, 48 percent to 40 percent. The poll surveyed 400 likely voters via live telephone calls between July 31 and Aug. 4.

The 1st District, located in the Hawkeye State's northeast, is the most Democratic House district in Iowa. President Barack Obama won there in 2012 by 14 points.

Democratic turnout in this district is crucial for Braley, who is currently locked in a Tossup contest against state Sen. Joni Ernst in the open-seat Senate contest this November.

Iowa's 1st District is rated a Safe Democratic contest by the Rothenberg Political Report/Roll Call.